Moisture resistant filaments of cellulose acetate



Patented Apr. 9, 1935 I i1,9 97,316 MOISTURE RESISTANT-FILAMENTS F .o LLULosE ACETATE 4;

' Paul se l; mea er, N. .Y., as sighor to East n wetmn o N l o N0 Drawing.

This inventionrelates to artificial filaments for textile and other purposes and particularly such filaments which have been prepared from cellulose. acetate having high moisture resistance.

Since the time ofIChardonnet and'his original artificial silk made of nitrated cellulose which was regenerated prior to weavingit hajs been the desire of investigatorsm this art to produce arti ficial silk filamentsv which would have high strength, whether in the wet .or dry state. Attempts to increase the wet strength of such filainents have" resulted in their manufacture from dissolved. cellulose and. from' the various types of cellulose esters, for example, the mixedcellulose acetate-nitrate, cellulose propionate, cellulose formate, etc., s well as inthe treatment of the formed. filaments which may have. been manufactur d by any of the usualpjrocesses, for instance,-the viscose or cuprammonium proc' esses, by the treatment of the filament either with "a sizing or other. water impervious layer to. inj hibit this loss of strengthwhile'the filament is in the moist condition. In spite OI these expedients of sizing coating ornimpfegnating of the filaments .orthe application of varioliawaterimpervious esters, of cellulose theretoythe' wet strength of the artificial filamentshas not been increased to the dry strength of the filament.

I have found thatthe preparation of artificial filaments from a solutionor' dope containing a particular type Y of moisture resistant cellulose acetate will produce a filament, due to this .unexpected resistance to moisture, of exceptional quality. The type'of cellulose acetatewhich I prefer to'use is of the acetone-soluble variety, which has been hydrolyzed to a particular degree, thus rendering it exceedingly more resistant to moisture than the usual acetone-soluble cellu lose acetate. The acetyl content of suchan acetate'will run-in the neighborhood oi from 38% to 42% andmay be prepared in any or the following described manners. I r I Artificial filaments, when prepared 'from this type of cellulose acetate, have increased wet strength due primarily to their great resistance acetate in acetone, with or without the use of the ordinary type of plasticizer such, for instance, as monochlornaphthalene triphenylphosphate, 'monoacetin or triacetin or similarplasticizers, will produce such a filament by extrusion into a heated chamber, whereby the volatilesolvent is removed and the filamentcoa'gulated. The filamentmay likewise be prepared, if desired, by an extrusion oi thedope into. a coagulating bath be employed with this exceedingly high precipii- "tat'ion valueacetateto impart the. desired plastomoisture. I have foundthat a solution of. this" Rochester, N. Y., a cori nr ication December, 24.,"1e29; SerialNo.4 16,286 n 6 Claims. '(01.

removes the lvolatile solvent contained, in the dope and likewisecoagulates the same.

. bath, if desired may be composed of ahsolution of asuitable-plasticizer' whereby this plasticizer is caused to penetrate-into the filament, sucha Q process being described inthe copendinafiPPfication of-Farrow et al. Serial No. 347,813 ffiled Mar. 18, 1929; r r I The cellulose acetate which I have foundto have these desirable characteristics may be pre-. pared gfrom any. type of cellulose triacetateI-such as that p d ced by. the, usual. pretr atinic an acetylatingmethods or, for instance',.by the proc ess as described in"U.,- .S; Patent No; 1,683,347, a yjLeflB'JC-ray and Cyril J. Stand, September 4, 1929 Thistrlacetate of Cellulose cohtaining approximately 44.8% acetyl is hydrolyzed either bythe addition jot aceticfacidand water or by the additionoiacetic' acid, water and a mineral f 1 acid catalyst or by the. production .W thinith'e acetylating bath. of water" which'may be efiected by the addition 'ofan jalcohol or othefrflwater former thereto 1 The cellulose acetate whichI prefer. tousfe is obtained by stoppingjthe hydrolysis. o: the cellulose ac'etate'fwhlen approximately 90% or more of a sample taken from the hydroly'zing solution, precipitates ma mixture of water and acetone by volumewhen' carried out in the manner described below. Cellulose acetate which has been accurately. hydrolyzedtothis degree has attained exceptional qualities .of water' resistance and good flexibility which are not "shown by any other cellulose acetates whicharesoluble in acetone. Furthermore, the addition of phenyl or, ortho cresyl v para toluene sulfonate,

triphenyl phosphate or tricresyl 'phosphatejto a cellulose acetate having a precipitationvalue of -97 per centwill' increase even rurtner the moisture. resistance of thev cellulose "acetate. 40 Above 97' per cent precipitation value littles'orno added moistureiiesistance Will beefiected by such an addition andany'io' f the usual plasticizers may ticity, very slight if any additional moisture: re.- sistance being efiective by their presence. In order'that'themethod of determining this particular point in the hydrolysis of the cellulose acetat maybe-morethoroughly understood the exact ethod used is here disclosed} Asam'ple'of] .the'} cellulose acetate which has been removed from the hydrolyzing reaction mixtureiis dried under standard conditions; to 5.00 grams ofthis driedcellulose acetate there are'added 100.0 cc.v

' be taken to keep the solvents and mixtures at a temperature of i1 C.,- wherever volumes are being measured. 7

At the end of the addition of the acetone-water solution, a mixture is obtained containing" 40%.

water by volume (neglecting contraction). in which is suspended the precipitated cellulose acetate. This is allowed to stand for 12 hours at20 C., and cc. of the clearest supernatant solution are removed with a pipette. At thefend of this time, precipitation has reached equilibrium and proceeds no further. This 25 cc.,portion;

is centrifuged in a stoppered bottle at a high speed until the liquid is perfectly clear. Exactly 5 cc. of the liquid are removed with a pipette and evaporated to dryness on a taredwatch glass. If W is the weight of the residuein grams, the precipitation value which equals the percent cellulose acetate precipitated'will equal =1'00'--1000W V a I" have found that "artificial filaments for the preparation of artificial silk or like products, as prepared from a dope containing a hydrolyzed cellulose acetate, that gives a preciptation value in the above test of 90% or better. have an ex ceptionallyjhigh water resistance, with. 'itscorresponding increase in, wet strength,;due' to this resistance towater. It will be understood that while this cellulose acetate artificial filament may not have an appreciably greater strength'when that strength is computed upon the percentage of moisture contained in the filament, nevertheless, by the useof this type of cellulose acetate, when compared to a cellulose-acetate filament subjected to equivalent moisture conditions, the wet strength of the filament prepared from my type of cellulose acetate will be decidedly greater. To obtain this desirable product, it is .but necessary to control the hydrolysis by the utilization of suitable hydrolyzing baths in fwhichthe .degree'of deacetylation and the precipitation value of the cellulose acetate may be readily and accurately controlled. The method of so controlling'this hydrolysis is described inthe U. S. Patent No. 1,878,953 ofCQJ. Malm.

The'precipitation value of 90% or more may be obtained by the usual hydrolyzing methods,

the hydrolysis be stopped at the correct point. When'this point has been reached, it is often very difiicult instantly tostop furthenhydrolysis application of C. J. Staud and J T. Fuess,'Serial No. 398,807 (Pat. No. 1,895,351) Other methods of effectively controlling the hydrolysis in'order that it may be stopped when the product has the required precipitation value may be employed. I

The following hydrolyzing processes which I call the facid final or water final have proved efficient. In the acid final type of hydrolysis mineral acids (i. e. hydrochloric or sulfuric acid) are added with acetic acid and water to the socalled "first stage cellulose acetate dope: i. e., the cellulose acetate solution attained at the end of the acetylating step, usually a solution of a fully acetylated celluose. The quantity of mineral acid added is adjusted so that hydrolysis requires from to hoursat a temperature of 95 to 100 F. At this temperature, it is somewhat diificult. at all times to regulate the exact time at which the hydrolysis should be stopped, as noted above, to 'give a precipitation value of 90%; at a ower.temperature, however, of say F., the time of treatmentis increased to from 5 to 10;,days .withtheresultant increase in the accuracy of control- Of the two hydrolyzing processes, I prefer, however, to use the water fina method which I will now describe. 7 This may be carried out by the use of acetic acid and water without the addition thereto of further mineralacid catalysts, as the catalysts from the first stage? of the acetylation are usually suificient. ,At a temperature of l0" F., hydrolysis conducted in this manner will require 20 to 25 days to obtain a product having precipitation value ,of approximately at ate'mperature of 90 to F., the time will-bereduced to from 8 to 12 da'.ys: It is apparent thatwith the'long period ofhydrolysis, as here described, and by the use of the process of Staud andtFuess for the'stopping of the hydrolysis, accurate deacetylation of the cellulose acetate may thus be obtained. After hydrolysis, the celluloseacetate may be isolated,washed,'and dried by any of the usual processesjand; after solution in acetone or other suitable solvent, with or without plasticizers, may beextrudedin' any of the well known methods forthepreparation of artificial filaments. Cellulose acetate of this type, therefore, may be prepared'from" any of theusual. acetylating solutions and formed by any of' the .well known processes into artificial filaments without in any wa departing from this invention or sacrificing any of its advantages.

Infthe claims hereunto appended, where reference is made to the precipitation value? of the cellulose acetate to be employed it will be distinctly understood that such value isaphysical characteristic of. the cellulose acetate which is to be determined'in accordance with the method above set forth in detail. The fact that the method of determining the precipitation value should be followed closely is not, of. course, to be understood-as limiting the scope of the invention since that is limited only bythe specified range of the precipitation value of the cellulose acetate to be employed. such as ndicated below, providing, of course, that While my product is primarily filaments cellulose acetate composed principally of acetonesoluble cellulose acetate having the above described degree of hydrolysis, I have found that otherfilaments composed of any of the usual types of. rayon,,such as viscose, coprammonium silk, and denitrated cellulose nitrate, may be rendered more moisture resistant if they be encased in a coating of this type of cellulose acetate. This maybe done bypassing the rayon in filament form through a bath-containing the cellulose acetate in solution. Y

What I claim as myinvention and desire to be secured by Letters Patent of the United States 1'. Artificial filaments of the rayon type having an unusual degree of resistance to moisture and increased wet strength essentially consisting of an acetone-soluble cellulose acetate having a precipitation value of at least 90%. a

2. Artificial filaments of the rayon type having anunusual degree of resistance to moisture and increased wet strength formed from a solution containing acetone-soluble cellulose acetate having a precipitation value of from 90% to 9 3. An artificial filament of the rayon type having an unusual degree of resistance to moisture and increased wet strength formed from a solution containing acetone-soluble cellulose acetate having a precipitation value of 1mm 90- 97% and o-cresyl para toluene sulfonate.

4. Artificial filaments of the rayon type havand increased wet strength formed from'a solution containing acetone-soluble cellulose acetate,

having a precipitation value of from 90% to 9'7 and triphenyl phosphate.

5. Artificial filaments of the rayon type having an unusual degree ofresistance to moistureand increased wet strength essentially consisting of acetone-soluble cellulose acetate having a preacetone-soluble cellulose acetate having a precipitation value of from 90% to 97% and a 

